1. The Field of the Invention
The present invention relates generally to fluid bed granulators, coaters and dryers. In particular, the invention relates to a filter apparatus including a movable filter bundle that can be selectively raised and lowered to facilitate maintenance of one or more filter units on the movable filter bundle.
2. The Relevant Technology
Granulation is a crucial stage in many industries, such as mineral processing, agricultural products, detergents, pharmaceuticals, foodstuffs, and specialty chemicals. It is a size enlargement process where fine powder feed particles are bound together to form agglomerates or granules, a process that, for example, enables the formation of tablets. One type of granulation, wet granulation, is a process where the particles are bound together by a fluid (also called a binder) which forms liquid bridges between the particles to hold them together. The binding fluid is usually a solvent, like water or ethanol, or a solution of a polymeric binder in a solvent.
A fluid bed granulator is a tall cylindrical or rectangular vessel containing a bed of particles. Air is forced through a distributor at the base which fluidizes and agitates the powder. A binding fluid is added by spraying from above, below, or within the powder bed. These binder drops collide with the powder particles and form liquid bridges, which hold them together by capillary suction. By heating the fluidizing air, the product can be granulated and dried simultaneously, which is particularly useful in the specialty chemical and pharmaceutical industries.
As a result of the processes, fluid bed granulators, coaters, and dryers create a large amount of dust that fills the process air used therein. In order to prevent the release of this dust to the environment these devices therefore require the use of filter systems.
One such filter system is a bag filter system as illustrated in U.S. Pat. No. 5,446,974 to Gubler, herein incorporated by reference. The Gubler patent discloses a filter assembly having a cylindrical fluid bed chamber wherein the process air enters from one end, is filtered by one or more bag filters, and exits the opposite end. The bag filters are rigidly attached to a mounting plate within the filter plenum during operation and are unattached and removed from the filter assembly for servicing.
The individual bag filters disclosed in the Gubler patent comprise flexible filter bags that are fitted over and clamped onto underlying rigid frames. During operation, the filter bags form around and through side bars of the rigid frame in an accordion shape. Periodic cleaning of the filter bags is achieved by applying a periodic pulse of reverse air to the bag filter, forcing the filter bag outward from the rigid frame and dislodging particulate matter that has accumulated on the filter bag. Although this is remarkably effective, the filter bag must be eventually removed and cleaned or replaced.
Of course, a variety of other filter assemblies, filters, and bag filters exist that can also be effectively used to filter process air. With each of these filter systems the degree of difficulty in cleaning or replacing a filter in a fluid bed system can increase costs and limit the operational time of the filter system and its corresponding fluid bed system.
The present invention relates generally to a filter apparatus for use with a fluid bed processor. The filter apparatus generally includes a fluid bed chamber, a filter mount transport mechanism within the fluid bed chamber, and a filter mount for receiving a filter. The filter mount transport mechanism typically has one or more filters attached to corresponding filter mounts on a support structure. The filter mount transport mechanism may also include an index rod that rotationally secures the filter mount transport mechanism when in the operational position. For example, in one embodiment of the invention, in a first position air is filtered through the filters in the process operation of the filter assembly and in a second position individual filters on the filter mount transport mechanism can be easily inspected, serviced, and/or replaced.
According to one embodiment of the invention the filter mount transport mechanism further comprises at least one filter unit to form a movable filter bundle. One preferred filter unit includes a rigid frame, flexible filter media positioned relative to the frame so that the flexible filter media extends at least partially through openings in the frame and into the rigid frame when the filter unit has process air flowing therethrough, and a mechanism to secure a portion of the flexible filter media to the rigid filter frame. This embodiment of the invention also may include a cleaning mechanism, intermediate to the outlet opening, for removing particulate matter accumulated on the flexible filter media by causing the flexible filter media to momentarily flex outwardly from the rigid frame such that the flexible filter media extends substantially outside the openings. One such cleaning mechanism is a blow down tube.
According to another embodiment of the invention the filter mount transport mechanism further comprises an index rod. In this embodiment the filter apparatus also further comprises at least one index rod receiver, such as a tube or ring, attached to the fluid bed chamber. The index rod receiver is configured to receive the index rod and thereby rotationally secure the filter mount transport mechanism in a desired orientation while in the first position. Preferably, the number of index rod receivers equals the number of filter units to ensure a desired alignment between the filter units and other elements of the filter assembly, such as blow down tubes.
One method for servicing a filter in a fluid bed system according to the invention comprises first providing a fluid bed chamber within a filter apparatus, the fluid bed chamber having a movable filter bundle in a first position within the fluid bed chamber, the movable filter bundle having at least one filter attached thereto. Optionally, a portion of the fluid bed chamber is swung outward away from the fluid bed system and a product container is removed, thereby creating a filter servicing open space. The movable filter bundle is then moved to a second position within the fluid bed chamber. In this second position the filter is inspected, serviced, and/or replaced.
According to one aspect of this embodiment of the invention, the first position comprises a raised position within the fluid bed chamber wherein the filter apparatus can be operational to filter process air and the second position comprises a lowered position within the fluid bed chamber wherein the at least one filter can be easily accessed for service.
Servicing the filter can comprise refurbishing a reusable bag filter unit by removing the filter unit from the movable filter bundle, removing the bag filter media from a substantially rigid frame, applying a different bag filter media to the substantially rigid frame, thereby refurbishing the filter, and attaching the refurbished filter to the movable filter bundle. Alternatively, the method can comprise simply changing filters by removing a filter from the movable filter bundle and attaching a different filter to the movable filter bundle. Yet another embodiment involves replacing the bag filter media on an underlying rigid frame that remains attached to the filter mount transport mechanism.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.